The present invention relates to a multiple sprocket assembly with a plurality of sprockets with different numbers of teeth for assembly on a rear axle of a bicycle, comprising a base body, on which at least a part of the plurality of sprockets is provided, and a support ring that is connected to or can be connected to the base body in a torque-transmitting manner. Furthermore, the present invention relates to a rear axle assembly for a bicycle with a multiple sprocket assembly of this type.
Various systems are known in the prior art for the attachment of multiple sprocket assemblies for bicycle gears on rear axles. In a widespread system, a driver is supported in a rotatable manner on the rear axle of a bicycle via a bearing arrangement. The driver is in torque-transmitting engagement with the hub shell via a one-way clutch and permits a torque transmission in the one direction of rotation (drive direction), whereas it is uncoupled from the hub shell with respect to rotation in the other direction in order to provide a free-wheel. Usually a driver of this type is provided on its outer circumferential surface with keyways or splines or a comparable profile, in order to be able to attach hereto individual sprockets or an assembly composed of several sprockets in a torque-transmitting manner. A solution of this type is shown in the prior art, for example, in DE 199 15 436 A1. Comparable solutions are further shown in documents JP 59-165293, GB 2 177 628 A or EP 0 277 576 A2.
Although this system is very widespread, it is increasingly reaching its limits and has disadvantages. For instance, particularly with sophisticated bicycle gear systems, such as are now used in professional bicycle racing as well as for recreational cyclists, the number of sprockets is constantly increasing. This is in part due to relatively large gear ratios being offered but in particular also relatively narrow graduations are used in order, for example, to render possible an optimal gear ratio when cycling over flat terrain or when cycling in a group with a constant pedaling rate. In both cases, i.e., when narrow graduations are provided with small gear ratio transfers or when large gear ratio steps are to be provided, there is an increasing need for smaller sprockets, i.e., sprockets with 10 teeth or less. Such small sprockets, however, can no longer be mounted on a driver of the conventional type, so that auxiliary constructions are necessary, which usually require additional parts and therefore have a complicated structure or are difficult to install.
Furthermore, the classic driver solution entails a further basic problem with respect to the power flow. It must namely be taken into consideration that the sprocket respectively wound about by the drive chain during the drive is exposed to strong transverse forces, which act along the chain. These transverse forces have to be absorbed via the bearing of the driver by the rear axle. In the known solution, the transverse forces have to be transmitted to the driver and by the driver via the bearing arrangement to the rear axle. At the same time, however, the torque must also be transmitted to the driver. This means that the transverse forces due to the chain force as well as the drive torque have to be transmitted via one and the same “interface” between the sprocket or sprocket set and driver. This interface is usually the splines embodied on the outer circumferential surface of the driver. It has been shown that this is associated with disadvantages, because due to the transverse forces occurring, a strain on the individual sprockets occurs, which then can have a negative effect on the torque transmission.
In the prior art it has already been recognized that—despite its widespread use—the conventional solution with a separately embodied driver, on which then individual sprockets or a set of sprockets are or is attached, is associated with disadvantages. For this reason alternatives have been sought.
For instance, document DE 20 2008 005 971 shows an arrangement in which a sprocket set is embodied in one piece with a pipe element. The pipe element for its part is used for bearing on the rear axle and has a functional section, on which the torque transmission takes place via the free wheel arrangement on the hub shell. Although this solution may have advantages regarding the bearing of the sprocket set, it has the fundamental problem that the force flow from the largest sprocket runs through the entire sprocket set to the smallest sprocket and from this through the pipe to the one-way clutch. This means that the entire sprocket set, in particular also the small sprockets, have to be embodied in a relatively solid manner in order to be able to durably withstand this power flow. The bearing tube inside the sprocket set must also be embodied in a correspondingly solid manner. The result of this is that the solution has to be embodied in a relatively solid manner and thus with a large weight.
Document DE 10 2009 006 101 A1 also tries to circumvent the conventional solution of a separate externally toothed driver. In this solution in turn a basic sprocket set with a relatively large number of sprockets is provided, which has to be embodied in a correspondingly solid manner for power transmission. In addition, a supplementary sprocket set can be screwed onto this base sprocket set. However, again it is shown that the entire power flow in particular from the heavily loaded sprockets with a large diameter, runs through a relatively long section of the sprocket set, so that the entire sprocket set has to be embodied in a correspondingly solid manner including in the region of smaller sprockets, which leads to the problems already mentioned above of a large total weight of the arrangement. Furthermore, it is not discernible with this solution that in fact the problem of accommodating very small sprockets has been taken into account. Also the additional sprocket set, which has rather smaller sprockets and is screwed onto the basic sprocket set, is embodied such that it is embodied radially outside a pipe section of the basic sprocket set. Thus a similar situation results as with a conventional driver.
Finally, document FR 896 001 shows an assembled sprocket arrangement that is composed of a plurality of individual parts. Basically this arrangement however again follows the idea of providing in particular the smaller sprockets on a type of driver, which is an obstacle as far as the dimensioning thereof with few teeth is concerned.